It is desirable that an operator of an X-ray CT apparatus control an exposure dose received by an object so as not to apply excess X-rays to the object. Thus, in order to control exposure doses received by objects, for example, a conventional technique has been proposed that total DLP (Dose Length Product) and maximum or average CTDIvol (volume CT Dose Index) are displayed for operators based on scan conditions.
A threshold level of X-ray exposure doses received by objects varies depending upon ages, sites to be photographed, and body types of the objects. However, conventional techniques control the exposure dose using a sum exposure dose from an overall scan. Thus, it is difficult for the conventional techniques to control the exposure dose depending upon a scan area of an object.